X-ray diffraction photometer



Dec. 6, 1949 E. F. CHAMPAYGNE ETAL 2,490,673

X-RAY DIFFRACTION PHOTOMETER Filed June 16, 1948 2 Shets-Sheet l ATTORN EY Dec. 6, 1949 E. F. CHAMPAYGNE ET AL 2,490,573

X-RY DIFFRACTION PHOTOMETER Filed June 16, 1948 2 sheets-sheet 2 l co/v 714C? COA/72167] i mi;

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/L v f ATTORN EY Patented Dec. 6, 1949 X-RAY lolrrimcTIoN11H0'roME'rER Edmund Francis'v Cham Charles L. Christ; Ol

American Cyanamid Company,

paygne, Norotoni Heights, d Greenwich,f andV Robert Bowling BarneafStamford; Conn., assignors'to New York,

N. Y., a corporation of Maine Application .lune 1.6, 1948,-S`erial N0.33,'318

infrared ranges by using the various types Iof recording flickering beam spectrophotometers. However, there has been rno simplesolution'of the similar problems presented by various diffraction patterns bothk X-ray and .electron and certain aspects of infrared analysis. The` type of solution presentedby the method and apparatus of the present invention isfapplicable to the visual fieldl as Well as the others referred'to above butbecause. theproblem is less acute in the visualeld dueto theavailability of simple recording comparison apparatus, the invention is of primaryimp'ortanceV in other elds.

The general type offsolution to iwhich the pres-- ent process and apparatus .is applicable. isfone;v where the responses to radiant energyof two-ori more samples are detected andtran'sformedinto electrical energy either currentor voltage..

Essentially.. the present invention Vrotates inl synchronism a plurality of samplesand electrical.

contacts bringingthe samples successively into the beam of radiant/energy. The vcontacts are so positioned that the responses from detectors ofradiant energy striking the two samples areA con-A nected to separate circuits or to opposite connections on a diierential circuit. The electricalresponse from the radiation detector receiving radiant energy from each sample vis thus'isolated and comparisons are obtainable.

The method and apparatus ofthe lpresentinvention have the advantage that comparative responses are obtained Which'are'not materially aiected by ambient changes in temperature, radiation sources, amplications and the like. In other words, in each cycle the method and apparatus may be considered as self-Calibrating.

This is an important practical advantage because many radiationsources are not constant either With time, frequency, or'both. Only with dickering beam-spectrophotometers in the visual and' near infrared and ultra violet regionslia's/any 2 comparable vdegree' of self=calibration been achieved.

While the'ffea-tures-of comparison and automatic calibration are` common'to `all of the modications of the present invention,.it is possible in ina-ny cases to ei'ect'at thesame-time ari-intensity increase or `amplificationrof response which for practicaly purposes may introduce a completely new typefofamplicationffhaving;'a factor of as much as l to fl'. Inamore specific aspect of the invention-combined comparison and 'inherent amplicationfis included. .T-he .ampliiication factor results wherethe-'l-radiant' energy is in the form of. pulses-havingihigh'erf peak values than average va1ues and:is-obtained vby. choosing a contact time for the contacts Which-corresponds only with a pre-determined `portion :ofthe pulsewhere the power4 of the'pulse is at amaximum or at a high average level.

' One of i the-mostimportantfiields of application ofthe present invention is in recording X-ray diffraction' spectrophotometers, f especially those in which X-raydifraction patterns'are scanned by a Geiger countertube` with Vaccompanying circuit; rihe invention will -therefore be described in greater detail inconju-nction with such a device, the. applicability 'co-similar problems involving other formsof..radiant energy-being brought-out during the discussion.

In an ordinary` recordinglX-ray spectrometer, for example,the typeWhichiscommercially available from the Phillips North American Company,

an :alternating current Y actuated X-ray tube is used producing afpulsating-beam of X-rays'consisting in pulses having a` cycle duration of lessthan 1rradiansof .the cycle. X-rays are only produced-on one-half ofy the sine Wave of alternating voltage andA aseach-l X-ray requires a certain thresholdvoltagefthe pulse does not start untilthe alternating voltage' has reached a certain minimum ligure The-beamcf X-rays strikes a suitablesample. such as a powdered material. A Geiger counter tube andthe sample surface plane are rotated in the-horizontal plane, the former at'twice the angular ratefof the latterso that the tube. .successively .scans successive diffraction bands or lines. VThe rate of movement of the tube is', of course, very small compared to the frequency of the X-ray pulses. During anyone X-ray-pulse j at the diffraction lines there are different amounts of quanta of '.X-rays, the quantum density being at a maiii'mum at th'e point ofmaximuin pulse energy. The Geiger tubeand associated circuits as usual counts each' quantum, producing an amplified electric pulse which is fed'into a recorder having a time constant so that the responses from the quanta are integrated. Such a circuit requires capacity and resistance and the response of the recorder thus constitutes the difference between the energy stored up from the Geiger contact circuit pulses during the time when an X-ray pulse strikes the sample less the average loss through leakage throughout the whole cycle, including a dead time between pulses of more than 1r radians. In the ordinary recorder, the output moves a pen over a slowly moving recording surface and a trace results which is proportional to the intensity of the various diffraction lines.

The common recording X-ray spectrometer will not give an accurate, comparative result for two or more samples except in a rough semiquantative way by running first one sample and then the other and comparing the graphs. This is a serious disadvantage. In the rst place scanning time is doubled and comparison time added. The graphs are not necessary quantitatively accurate because back ground noise and changes in X-ray radiation electrical supply to the amplying circuits all contribute to the graph produced and make an accurate and fast quantative comparison impossible.

When the method and apparatus of the present invention is used, two or more samples are alternately introduced into the X-ray beam, for example, by mounting them on a rotating plate, each sample being in position so that it receives only a single X-ray pulse. At the same time electric contacts are actuated in synchronism so that the Geiger counter output when each sample is in the X-ray beam is directed to a separate recording circuit or to separate branches of a suitable dilerential recording circuit. For example, the record of the pulses from one sample may be downward from a central chart line and the other upward.

A very accurate comparative measurement is obtainable because the samples are compared by exposure to successive X-ray pulses, the exposure time being so short that there is no substantial change in radiation intensity, the device, therefore, constantly calibrating itself. Y

More than one sample may be used with a cor- Y responding number of contacts but for most operations it is not necessary to compare more than two.

In an infrared spectrophotometer, the problem of obtaining an accurate infrared spectrogram is caused by the fact that the intensity of infrared radiation Varies with frequency, therefore, an infrared absorption or transmission curve must be compared point by point against a curve of the emission of the source in order to obtain a record of the absorption of the sample. The method of the present invention avoids such a time consuming operation. It is only necessary to introduce the sample periodically into the infrared beam and introducing the response of the radiation detector, which may be a thermo-couple or a bolometer through the contacts into a diierential recording circuit so that a record is always obtained which is the difference between signal from the infrared beam itself and that from the beam passing through the sample. A curve can then be recorded which gives infrared absorption with frequency directly.

In each case where the comparison effect of the present invention is used, it may be combined with an amplifying effect when the contacts are adjusted to correspond to the portion of the cycle in which maximum energy is being radiated.

f sponse to a single diffraction line with two samples.

Fig. 1 shows the application of the present invention to a typical X-ray diffraction spectrom- Ieter of the recording type. The X-rays appear from the left from a conventional pulsating source (not shown) and strike samples in holders 2 and 3 which are mounted on and project above a plate I. The beam strikes the samples at an angle within the range usually employed for X-ray diraction measurements. The plate I is mounted on a shaft 4 which is rotated by the motor 5. A Geiger counter tube 6 receives X-rays dilracted from the samples and features an amplier of conventional design. The plate I and tube 6 are movable about a vertical axis through the center of the samples by the usual means in X-ray spectrometers. For clarity these are not shown as they are not changed by the application of the present invention and therefore do not constitute any part thereof. As is usual, the rate of angular movement of the Geiger counter 2 is double that of the sample holders in the horizontal plane in order to match the doubling of the angle of diffraction. The scanning eect is obtained as in ordinary X-ray spectrometers. A second position corresponding to a particular X-ray diffraction line is shown in the drawings.

The rotation of the plate I successively brings the two samples into the X-ray beam and is synchronized at one half the frequency of the X-ray source so that each sample is brought into the beam during successive single X-ray pulses. The motor also turns a cam I0 provided with followers II which successively open and close contacts 8 and 9. These contacts serve to connect the ungrounded side of the output of the amplifier 'I to opposite sides of the input circuit of the recorder I2. The latter is of conventional design. As shown in the drawing, the output voltages of the amplifier are developed across equal condensers I3 and I4, the time constant of the recorder being greater than pulse frequency. The cam is adjusted so that the contacts are closed in the center of the X-raypulse for each sample. The recorder, therefore, receives a voltage which is the differential of that produced by the Geiger counter when scanning the diffraction lines of the two samples. It will be apparent that a comparison is made every revolution of the plate I, the time involved being so short that no changes in average X-ray pulse intensity result. In other words, the device makes a comparison every cycle and is thus constantly calibrating itself.

Most samples which are examined for X-ray diffraction are solids which may be powders. The drawings illustrate sample holders suitable for use with such materials. It is, however, sometimes desirable to measure the diffraction patterns of liquids and other materials which are not suiciently cohesive to be retained in the ordinary type of sample holder illustrated. In such cases the sample holders may be provided schoolers witha-suitable'rcoverfior material` Whichls transparent-to X-rays f andy does not itself;` give a1 diffraction patternwhi'ch would-maskthat of the and the position of the contact elements. The ,f contact time may be adjusted from something less than one pulse cycle to a much smaller fraction. This is'shownin iFig.`3 where three pulses of uniform amplitude are shown. lIn

terms of the frequencyiofv'the alternating current of the X-ray tube, each pulse lasts for less than one half a cycle, actually as shown about =140. This is because no X-rays are emitted until the alternating voltage lreaches acertain threshold value in the positive wave of the cycle. This leaves some 220 of the cycle during which there are no X-rays. This is usually referred to as the dead time.

If the contact time is very long, for example 280 as shown for the first X-ray pulse, the Geiger counter tube 6 will feed voltage into the ampliiier and thence into the recorder only for 140 and the average level of this voltage during this time will be a fraction of the peak voltage.

Since the recorder has a circuit involving a time constant, energy leaks olf the charging condenser during the dead time and even during the portion of the actual pulse when the voltage is below peak voltage. Amplier and recorder will, therefore, give an average response which is shown by the small rst peak in the bottom curve of Fig. 3. When the contact time is decreased to 140 as shown in the second pulse in Fig. 3, there is no leaking of energy during the dead time and a much stronger pulse is observed, actually a pulse which is somewhat more than twice as great as in the case of the 280 contact time. The third pulse in Fig. 3 shows the eiect of a 40 Contact time which corresponds to the peak portion of the pulse. No leak results during the time of lower energy and during the dead time and a much greater response is obtained which is shown as about four times ior the 280 contact. This latter corresponds to the situation encountered in the ordinary X-ray spectrometers known hitherto. The increase in ampliilcation is almost four times. Theoretically, an amplification factor of four can be obtained, but usually practical design consideration make a contact time of less than about 40 undesirable.

Figs. 4 and 5 show the effect of a differential recorder circuit such as that illustrated in Fig. 1. Curves A and B of Fig. 4 represent energy pulses from the amplifier I corresponding to X-ray diffraction lines of tWo diiferent samples. These are not responses from a single X-ray pulse as the scanning rate of the recorder is such that each band encounters a large number of X-ray pulses before the slow moving Geiger tube 6 passes it. Curves A and B, therefore, represent the type of curves which would be drawn by an ordinary recording spectrometer.

When the arrangement in Figs. 1 and 2 is employed, these two curves are scanned simultaneously, iirst one sample being in the beam and then the otherpandsthe recorder recordsthe energy responses in a diierential circuit, the recording -element'.beingfadjusted `so that the base lines in 'thel curves in Fig..` 4

represent the neutral point of thediilerential'circuit. The energy from the 'ir'st sample represented by curvefA tends to move the recording element Vof the recorder that of B down.

` up and The resulting differential curve iis Shown at C. It "will-be noted lthat in the case lo f.

ofthe first-and last lines of curve A there is no corresponding line in curve B and these are, therefior-e," reproduced above the neutral line in their natural height in curve C. The third and sixth bands appear only in curve B and are reproduced fin curve C in 'their natural size below the line. :The-second 'bandi represents asituation where there isa slightly stronger line in curve A than fin curve- B. vTheresult is a small diierential response in curve C in the direction of the strong- 'erf line. The fourth line represents a similar situ- -ation ini which' the 'difference between curve A and cu'rvel B is large' and here the differential response -is considerably greater than in the case of the second line. Fig. 5 shows graphically how .thisl latter kresult is obtained.

The invention has been illustrated in conjunction with an X-ray diffraction spectrometer. The same type of response can be obtained in an electron diiraction device using electron beams in an evacuated vessel.

The lrecorder in Fig. 1 is shown ias a straight differential recorder. For many purposes this is the most useful type. However, it is not necessary that ithe differential circuit be of this type. Other conventional differential circuits which give ratios between two iamlplier outputs may also be used. The nature of the circuit in the recorder forms no part of the present invention and it is an advantage that the features of the present invention may be lused with any conventional diiferential or other recording circuit.

In Fig. 1 the carn actuating the movable contacts is shown as driven from a shaft actuated by the same motor which turns the sample holder plate. This is a more compact arrangement presenting some advantages. On the other hand, the whole mechanism has to be rotated and vfor certain `purposes it is desirable to drive two synchronous motors, one operating the contacts and the other rotating the plate carrying the sample Iholders. The operation is, of course, identical Iregardless 0f whether the synchronism of the contacts land sample holder plate rotation is effected by rigid mechanical connection or by synchronous electrical connection.

We claim:

1. A comparison ydevice for comparing radiant energy responses from a plurality of samples comprising in combination means for producing a pulsating beam of radiant energy, means synchronized therewith for introducing sample holders successively into the beam during successive radiant pulses, a radiant detector positioned to receive radiation from said sample holders when introduced into the pulsating ybeam and capable of transforming :the radiant energy into electrical output, indicating means responsive to said electrical energy, circuits including movable contacts connecting said indicating means to the electric output of said detector and means operating in synchronism with the sample holders to close the movable contacts during at least a portion of each radiant energy pulse.

2. A device according to claim 1 in which the indicating means constitutes a recorder with a differential input connected tothe movable contacts.

3. In an X-nay diffraction spectrometer comprising a. pulsating X-ray beam striking a sample holder and means for rotating said sample holder and a Geiger counter scanner, the latter moving at twice the angular rate of the former, the improvement which comprises a movable and rotatable element provided with a plurality of sample holders, means for moving said element in synchronism with the X-ray pulse to introduce successively differennl sample holders into the :beam during said lpulse, a plurality of movable contacts, connections from the output of the Geiger counter amplifier to said contacts, and means `operating in synchronism with said sample holder means to close a contactduring a1; least a portion of the exposure of each sample holder to an X-ray pulse. y

4. A device according to claim 3 in which the element provided with sample holders is a rotating plate driven by a synchronous motor.

5. A device according to claim 4 in which a recorder with a diierential input circuitl is provided and the movable contacts are connected to the sides of said differential circuit wherebythe recorder receives an output which is la diierential between difiracted X-rays from said sample holders when holding samples.

EDMUND FRANCIS CHAMPAYGNE.

CHARLES L. CHRIST.

ROBERT BOWLING BARNES.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,074,226 Kunz et al Mar. 16, 1937 2,394,703 Lipson Feb. 12, 1946 FOREIGN PATENTS Number Country Date 506,022 Great Britain May 22, 1939 OTHER REFERENCES Review `of Scientific Instruments, Sept. 1946, p. 345 by E. F. Champaygne. 

